1. Field of the Invention
The present invention relates to conveyor lubricants compatible to P.E.T. containers, i.e., containers made of ethylene terephthalate homopolymers, copolymers and mixtures thereof. More particularly, the present invention concerns the methods and use of compositions of emulsifying agents, alkyl phosphate esters, alkyl aryl phosphate esters, fatty acid, potassium hydroxide and optional inorganic phosphate as conveyor lubricants. Even more particularly, the present invention concerns concentrates prepared therefrom, and the methods and use thereof of aqueous dilutable lubricant concentrate solutions for the transport of "P.E.T." containers along conveyor systems.
As is known to those skilled in the art to which the present invention pertains there has been an increasing usage of P.E.T. containers for beverages and other foodstuffs. Such containers are normally filled by passing them through filling and capping stations controlled conveyor systems.
To ensure proper operation of the filling and capping systems it is vital that the conveyor systems be continuously lubricated. Without adequate lubrication, the containers may stack up along the conveyor system and their movement impeded.
Thus, the conveyors are continuously lubricated by applying to the conveyor a lubricant, such as by spraying or the like. Conventional lubricants contain amines, alcohols, potassium hydroxide and other constituents which in various combinations are incompatible with the P.E.T. containers disposed along the conveyor system causing them to eventually crack in transit or storage.
Indeed, it has long been known that exposure by such P.E.T. containers to incompatible lubricants leads to a phenomenon which has been identified as "stress crack failure".
As noted, conventional aqueous-based lubricants containing alcohols, potassium hydroxide and/or amines do not inhibit or prevent stress cracking in P.E.T. containers, but rather promote stress cracking. More particularly, the use of potassium hydroxide as the saponifying agent, in fatty acid lubricants, has been found to contribute to and to promote stress cracking in P.E.T. bottles.
2. Description of Related Art
As disclosed in Wider et al. U.S. Pat. No. 5,009,801, it has been found that stress crack inhibitors, such as sodium xylene sulfonate, do not preclude and overcome the cracking caused by potassium hydroxide. Potassium hydroxide is a widely used component in commercial conveyor lubricants which is plentiful and economical.
Further, U.S. Pat. No. 5,009,801 disclosed the "stress cracking" inhibitor as selected from the group consisting of sodium xylene sulfonate, sodium decyl diphenyl oxide sulfonate, sodium dimethyl naphthalene sulfonate, sodium salt of a linear alkyl benzene sulfonate, and mixtures thereof, and the use of free-base alkyl amine as the saponifying agent. This art has not directed itself to the use of potassium hydroxide as the saponifying agent in the use of lubricant concentrates to be applied to P.E.T. bottles, and/or the use of alternative stress inhibiting agents as described herein.
As disclosed by Rossio in U.S. Pat. No. 5,073,280, which incorporates by reference U.S. Pat. No. 4,929,375, the alkyl aryl sulfonate, per se, is not always essential to the prevention of stress cracking of P.E.T. bottles. Rather, it discloses that a certain class of amines, with a sufficiently large molecular size, will inhibit stress cracking without the presence of the alkyl aryl sulfonate, and additionally smaller molecular weight amines consisting of at least six carbon atoms along with an alkyl aryl sulfonate will inhibit stress cracking of P.E.T. materials. The present invention does not make use of a high molecular weight or smaller molecular weight alkyl amines as the stress cracking inhibitor and saponifying agent as described in Rossio. None of the inventions discussed thus far have pH values which range between 9 to 10.5. The disclosure herein is not anticipated by this patent.
Sharf in U.S. Pat. No. 5,062,979 describes a substantially soap free lubricant containing a neutral (pH 6-8) composition of alkylbenzenesulfonates, partial phosphate esters with alkoxylated aliphatic alcohols, and aliphatic carboxylic acids. Sharf describes a lubricant concentrate usage within a neutral pH range (6-8), which is directed to the prevention of the occurrence of lime soap formation. Sharf's disclosure does not address the problem solved by the disclosure herein nor does Sharf anticipate the full composition or methods described herein.
Anderson teaches in U.S. Pat. No. 521,321 methods of preparing an alkyl phosphate ester conveyor lubricant containing a desired monoalkyl phosphate ester and small amounts of a dialkyl phosphate ester containing C12 to C20 atoms, whereby the composition is neutralized with a base ammonia, ammonium hydroxide or other water-soluble amine. This invention does not address its compatibility for use on P.E.T. containers, stability thereon, or compositions similar to that of the herein disclosure.
Other patents which are distinguishable from this disclosure are U.S. Pat. Nos. 3,583,914; 3,860,521; 4,604,220; 4,769,162; 4,839,067; primarily in as much as none refer to stress crack inhibitors in their claims nor do they set forth compositions which anticipate the disclosure herein.
The invention herein responds to the complaints of beverage bottlers regarding current P.E.T. lubricants in the market place. The current P.E.T. lubricants provide, as a class, inadequate lubrication despite their claims to the contrary, resulting in falling P.E.T. bottles on the conveyor filling and packaging system. This causes undesirable loss of production to the filling and packaging operation. In addition, the current P.E.T. lubricants cause accumulation of foam which creates an undesirable appearance.
Furthermore, in many instances the P.E.T. lubricants are not effective in preventing stress cracking. In other instances, some P.E.T. lubricants use expensive agents to achieve P.E.T. bottle compatibility in lieu of using standard saponifying agents such as potassium hydroxide. Consequently, the present invention solves a different combination of problems than the prior art compositions, allows continued use of potassium hydroxide, and provides novel properties which prevent or inhibit stress cracking in P.E.T. containers.